public static function destroy_volatile_caches() {
        global $SESSION;
        if (is_array(self::$volatilecaches) && count(self::$volatilecaches)>0) {
            foreach (self::$volatilecaches as $area) {
                $SESSION->navcache->{$area} = array();
            }
        } else {
            $SESSION->navcache = new stdClass;
        }
    }