1. In a computing environment, a method of servicing a DNS resolution request from a client, the method comprising: receiving at a server, a request from a DNS client, the request identifying a domain name to be resolved for the client, and wherein the domain name comprises a domain name that is not able to be resolved by the server as the domain name does not correspond to a record for a domain name that can be resolved by the server; identifying a hash of the domain name as being part of a set of hashes, each of the hashes in the set of hashes being hashes of domain names that cannot be resolved by the server, and wherein the hash of the domain name identified at the server was computed using a first cryptographic technique, but wherein the hash can be computed by an external system using a second cryptographic technique and wherein the first cryptographic technique is able to compute the hash in substantially fewer or substantially less complex operations than the operations required to compute the hash using the second cryptographic technique; and as a result of identifying a hash of the domain name at the server as being part of the set of hashes, returning a result indicating that the domain name cannot be resolved, including returning an indicator identifying the set of hashes.