I made a similar idea I thought it was stupid at first.
In a game with monsters and creatures free to go from any place is more than natural the formation of agglomerates for many reasons (Bugs, something that attracted them like sounds/players, Griefing or same for purposeful reasons), and when this cluster occur is when my idea enter into job.
one AI than kill this large amount of zombies. or a mechanism than disperses the same.
Go suppose than exist many zombies than normal in one region for example 200 Zombies than one player concentrate in there for any reason and he had a tragic death, okay, now how zombies are more powerful than in 3.0 and nobody wants to get close to 200 Zombies 2 or 1 or this area continue infected forever OR one tool of clean space go work.
How entity clean tools in games are very diversified I go propose many from the same purpose.
1 - Mechanic - If zombies concentrate in a point for a certain period of time they simply go disappear and eventually respawn in another place.
2 - Mechanic - If zombies concentrate in a point for a certain period of time these zombies go spread naturally.
3 - AI - If zombies crowd go start a carnage from the same killing yourselves.
4 - AI - if zombies crowd they will merge creating zombies more powerful and than go spread naturally
5 - AI - if many zombies crowd in a region one military helicopter go fly from the direction of agglomerate killing every zombie in the way if provoked enter in a fight with players.
6 - AI - If many zombies in a region airplanes go circulate the region 2 or 3 times and after this go drop bombs of area effect killing everything (Inclusive trees and players in these areas) players on houses they will be safe.
i wanted place a nuke on 7. idea but… well you know…
This is all.