Isn't there something stronger than simple excommunication? Interdicts, anathemas, etc?
Interdicts are issued against whole peoples. One might, for instance, issue an interdict against Boston. An anathema, however, may be more appropriate; essentially an anathema is similar to excommunication, but it took on a further meaning in that the anathematized was not only cut off from Communion (like Protestants), but even from Baptism (like pagans)!