1. A computer-implemented method, comprising: receiving, from a client, a request for content; determining, with at least one processor, whether a cached version of the requested content is stored in a memory device, the cached version of the requested content reflecting a version of the requested content as of a particular time or date; sending a validation request to an origin server when the cached version of the requested content exists, the validation request including at least information indicating whether the client is associated with at least one of a plurality of different categories of clients and header information based on the cached version of the requested content; and receiving a validation response from the origin server if the client is associated with at least one of the plurality of different categories of clients, the validation response including: an instruction to provide the cached version of the requested content to the client if the requested content has not been modified since the particular time or date of the cached version of the requested content; and an instruction to provide a current version of the requested content to the client if the requested content has been modified since the particular time or date of the cached version of the requested content.