(d) If a directly associated cost is included in a cost pool that is allocated over a base that includes the unallowable cost with which it is associated, the directly associated cost shall remain in the cost pool. Since the unallowable costs will attract their allocable share of costs from the cost pool, no further action is required to assure disallowance of the directly associated costs. In all other cases, the directly associated costs, if material in amount, must be purged from the cost pool as unallowable costs.