/** Mark nodes dirty for every zone with moving portal in the scene */
	void PCZSceneManager::_dirtyNodeByMovingPortals(void)
	{
		PCZone * zone;
		ZoneMap::iterator zit = mZones.begin();

		while ( zit != mZones.end() )
		{
			zone = zit->second;
			// this call mark nodes dirty base on moving portals 
			zone->dirtyNodeByMovingPortals(); 
			// proceed to next zone in the list
			++zit;
		}
	}