If you want the *CONTROLLING* of what gets loaded next in the IFRAME to be done by the outer window and not by the server-side code in the <IFRAME>, then you could instead have the server-side code "tell" the outer window that it is done. That is, it could spit out a simple JavaScript function call that calls some
JS function in the outer window.
This is more complex that the simple redirect that ssteward suggested, so I'd only suggest it if you need some sort of overall controller mechanism.