Using a custom controller, you can set the finish location for a Flow. Imitate a new page reference by passing the URL (as string) to define the location, as shown in the following controller example:

public class FlowRedirect { 
    public PageReference getPageA() { 
        return new PageReference('/001'); 
    } 
}

The following is the code for the Visualforce page that uses a custom controller and sets the Flow's finish behavior:

<apex:page controller="myFlowController"> 
  <flow:interview name="flowname" finishLocation="{!pageA}"/> 
</apex>

Using the preceding options, you can redirect Flow users to another page/URL but not a URL that is external to your Salesforce organization.