public function augmentValidURLSegment()
    {
        // If this page is being filtered in the current subsite, then no custom validation query is required.
        $subsite = Subsite::$force_subsite ?: SubsiteState::singleton()->getSubsiteId();
        if (empty($this->owner->SubsiteID) || $subsite == $this->owner->SubsiteID) {
            return null;
        }

        // Backup forced subsite
        $prevForceSubsite = Subsite::$force_subsite;
        Subsite::$force_subsite = $this->owner->SubsiteID;

        // Repeat validation in the correct subsite
        $isValid = $this->owner->validURLSegment();

        // Restore
        Subsite::$force_subsite = $prevForceSubsite;

        return (bool)$isValid;
    }