Need help in some triggers!!

Need help in some triggers!!

Ok, I am starting a map where u can go from one map to another, and then back to the original, but i dont know how(if it is possible) to cross common units(not heros) between those maps. IE. To take, togheter with the hero, some footmen and knights from the great city, to the dark florest, and then back to the first.

I would appreciate ur help, and, of course, put ur name in to the credits.

use the game cache to do so, check this topic