Units with the heretic trait have a 20% * heretic level chance each turn to reduce the dominion strength in the province they are in by 1.

Example: A Heretic(3) in a province has a 60% chance to reduce dominion strength by 1, with 3 Heretic(2) commanders in a province there are 2 40% chances of the dominion strength being reduced.

A heretic in a province with 0 dominion strength has no effect.