dh at argosign dot de - 
it is possible to unset globals from within functions thanks to the $GLOBALS array:

<?php
$x = 10;

function test() {
    // don't need to do ' global $x; '
    unset ($GLOBALS['x']);
    echo 'x: ' . $GLOBALS['x'] . '<br />';
}

test();
echo "x: $x<br />";

// will result in
/*
x: 
x:
*/
?>