on my site i just push the user off to
logout.php
where the page just simply reads
<?php
session_start(); //start session
session_unset(); //unset session
session_destroy(); //then trash session
header("Location: ../index.php"); //push to other page
?>
This code goes above the <html> tag at top of page
so this page would then Kill all the frames as you would load the link like
<a href="logout.php" target="top">Log out</a>
this should work