The best, only, way to find out if their excommunicated is to go to the Pope-O-Meter. Once your their, put your mouse cursor over the coss axis of a faction and wait a couple seconds. You'll get a popup that will tell you the current popes feelings about that faction. It will also mention if their excommunicated, or if the pope just loathes them. Having 0 crosses doesnt mean their excommunicated, but its a good indicator to check into it further.