PHP Destroying the current session completely

Here is a code snipper I got out from Janet Valade's PHP & MySQL Visual Blueprint book and this is what I use it to implement logout pages

---

session_start();
$_SESSION = array();
if (isset($_COOKIE['PHPSESSID']))
    setcookie('PHPSESSID', '', time() - 42000, '/');
session_destroy();

$return_url = 'login.php';
header("Location: http://".$_SERVER['HTTP_HOST']
                      .dirname($_SERVER['PHP_SELF'])
                      ."/".$return_url);
exit;