PHPの完全に私のメモですので、どうぞお気になさらずに。

<?php
session_start();

$_SESSION = array();
if(ini_get("session.use_cookie")){
	$params = session_get_cookie_params();
	setcookie(session_name(), "", time() - 4200, 
		$params["path"], $params["domain"],
		$params["secure"], $params["httponly"]
	);
}

session_destroy();

setcookie("値", "", time() - 3600);

header("Location: login.php");
?>