A computing resource service receives a request. In response to the request, the computing resource service queries a probabilistic data structure for an entry corresponding to the request. The computing resource service obtains, from the probabilistic data structure, a value that corresponds to the entry. Based at least in part on this value, the computing resource service determines whether the entry has expired. If the entry is expired, the request is fulfilled. However, if the entry has not expired, the request is denied.