public virtual class PageControllerBase{
//This is an extension to the PARENT controller.
    
    private ComponentControllerBase myComponentController;
    //a map to interact with multiple components (children)
    private Map<String, ComponentControllerBase> componentControllerMap;
    
    public virtual ComponentControllerBase getMyComponentController() {
        return myComponentController;
    }
    
    //getter for multiple components (children)
    public virtual Map<String, ComponentControllerBase> getMyComponentControllerMap() {
        return componentControllerMap;
    }
    
    public virtual void setComponentController(componentControllerBase cController) {
        myComponentController = cController;
    }
    
    //setter for multiple components (aka children, with a key to the controller)
    public virtual void setcomponentControllerMap(String key, componentControllerBase cController) {
        if (componentControllerMap == null) {
            componentControllerMap = new Map<String, componentControllerBase>();
            componentControllerMap.put(key, cController);
        }
        else {
            componentControllerMap.put(key, cController);
        }
    }
    
    public PageControllerBase getThis() {
        return this;
    }   
}

public virtual class ComponentControllerBase {
    
    //For key/pagecontroller pairs
    public String key {
        get;
        set {
            if (value != null) {
                key = value;
                if (pageController != null) {
                    pageController.setComponentControllerMap(key, this);
                }
            }
        }
    }

    public pageControllerBase pageController {
        get;
        set {
            if (value != null) {
                pageController = value;
                pageController.setComponentController(this);
            }
        }
    }
}

public class MyComponentController extends ComponentControllerBase {
	public User user;
	public Id userId;

	//Getters/Setters
	public Id getUserId() {
		return userId;
	}

	public void setUserId(Id i) {
		userId = i;
	}

	public User getUser() {
		if (user == null) {
			init(userId);
		}
		return user;
	}

	public void setUser(User u) {
		user = u;
	}

	public void saveUser() {
		update user;
	}

	//Initialize OR *Re-Initialize* this component. This is the key to a refresh/re-render. A query is made and The setters are recalled.
	public void init(Id uId) {
		User u = queryForUserSettings(uId);
		setUser(u);
		//setNotificationBooleans(u);
	}

	private User queryForUserSettings(Id uId) {
		return [select Id, 
					Receives_Weekly_Digest__c, 
					New_Offer_Notifications__c
				from User
				where Id = :uId limit 1];
	}
}

<apex:component controller="MyComponentController" allowDML="true">
  
	<h1>Contact Settings Component</h1>
	<div>
		<apex:attribute name="keyAssigned"
                                type="String"
                                assignTo="{!key}"
                                description="The key given to this component so the page can easliy get access to it." />

        <apex:attribute name="PageControllerBaseCalling" 
                          type="PageControllerBase" 
                          assignTo="{!pageController}" 
                          description="The controller for the page." />

        <apex:attribute name="usrId" 
        				description="Relevant User." 
        				type="Id" assignTo="{!userId}" 
        				required="true"/>

        <form>
		  	<apex:outputPanel>
		  		<li>	
		  			Receives weekly digest&nbsp;<apex:inputcheckbox value="{!User.Receives_Weekly_Digest__c}"/> 
		  			New offer notifications&nbsp;<apex:inputcheckbox value="{!User.New_Offer_Notifications__c}"/>
		  		</li>
			</apex:outputPanel>
		</form>
	</div>
</apex:component>

public without sharing class MyPageController extends PageControllerBase {
	public Id userId {get; set;} 
	public MyComponentController componentOne {get; set;}
	public MyComponentController componentTwo {get; set;}

	public MyPageController() {
		userId = UserInfo.getUserId();
	}

	public PageReference callComponentOneSaveUser() {
		System.debug('Saving the first component');
		componentOne = (MyComponentController) getMyComponentControllerMap().get('ComponentOne');
		componentOne.saveUser();

		//force the second component to re-render!
		componentTwo = (MyComponentController) getMyComponentControllerMap().get('ComponentTwo');
		componentTwo.init(UserInfo.getUserId());
		return null;
	}

	public PageReference callComponentTwoSaveUser() {
		componentTwo = (MyComponentController) getMyComponentControllerMap().get('ComponentTwo');
		componentTwo.saveUser();
		return null;
		//notice how there isn't an init call here. The first component will lag behind this one.
	}
}

<apex:page controller="MyPageController">

	<h1>Parent Page</h1>
	<p>
  		This is the Parent page. This page will drive the actions of the child component.
  	</p>
  	<br/>
  	<br/>
	<h2>First Component - Saving this will refresh the second component</h2>
	<br/>

	<apex:form >
	  	<c:MyComponent PageControllerBaseCalling="{!this}" keyAssigned="ComponentOne" usrId="{!userId}"/>
	  	<apex:commandLink action="{!callComponentOneSaveUser}" value="Save"/>
	</apex:form>

	  <br/>
	  <h2>Second Component - Saving this will NOT refresh the first component</h2>
	  <br/>

	<apex:form >
	  	<c:MyComponent PageControllerBaseCalling="{!this}" keyAssigned="ComponentTwo" usrId="{!userId}"/>  
	  	<apex:commandLink action="{!callComponentTwoSaveUser}" value="Save"/>
	</apex:form>  
	
</apex:page>