Possible to see zone completion when not in a zone?
Not that I’m aware of.
Personally I’ve been keeping a spreadsheet with a list of zones, and my characters. Check off each zone as I complete it. I find it rather tedious to check zones — even if we’re not considering money. For instance, checking 8 alts to see if they’ve completed all 6 cities costs no coin, but would take a large chunk of time.
I do occasionally check the map from somewhere else. I might look at the Queensdale map while standing in Lion’s Arch. Most of the time I can get a good idea of whether or not the zone is complete (particularly if there are obvious missing things like unfilled hearts or skill points or unexplored areas). But that’s the closest I’ve found to checking outside the region.
Hmm, maybe I’ll start a spreadsheet too. Though this seems like something obvious that Arenanet could easily implement. Putting it into the Achievements window would be an obvious move.