1. A nested transaction rollback method comprising: detecting a violation of a block of memory accessed within a set of nested transactions; retrieving a tentative rollback level for the violation; discarding a speculative state for the block of memory at each level of the set of nested transactions up to and including the tentative rollback level; refining the tentative rollback level to a lower level in the set of nested transactions; and, additionally discarding a speculative state for the block of memory at additional levels in the set of nested transactions up to and including the refined rollback level.