Also, the papacy is somewhat affected by the home country of the pope I think. At least I had an experience in my English grand campaign that a danish born pope seemed to tolerate the Danish attacking me for a long time without calling them off. I think the danes attacked me on several occasions and only after a long war they were excommunicated, I refrained from agrression and only defended against them, or attacked when the avoid excom type mission was not active.

Many other factions in similar situations have relented as I have waited for the pope to call them off at the threat of excommunication - usually one or two turns I just sit tight in the castle. If they assault, I usually win without a hitch as I tend to garrison my border provinces quite heavily. If they have not withdrawn their sieging troops they have ofter been excommunicated making them free game for me.