1. A method performed by a distributed system comprising a plurality of servers including a first, a second and a third server operable to communicate over one or more computer networks, the method comprising: at the first server: receiving a request for particular content from one of a plurality of clients, the request comprising a domain name; sending the request for particular content to the third server; in response to the request, receiving a message that comprises the particular content and one or more tokens distinct from the particular content; storing the particular content in a local cache of the first server in association with the one or more tokens; sending a subscription request to the third server, the subscription request comprising a request to receive invalidation messages for tokens associated with the domain name over a subscription channel associated with the domain name; at the second server: receiving a write request from any of a same and another one of the plurality of clients, the write request comprising the domain name; sending the write request to the third server; receiving a response to the write request from the third server; at the third server: sending the response to the write request to the second server; determining that the response to the write request is associated with a particular token; upon said determination, sending an invalidation message for the particular token to the first server, the invalidation message sent over the subscription channel for the domain name; at the first server: receiving the invalidation message for the particular token from the third server, and upon said receipt, determining that the particular token is one of the one or more tokens associated with the particular content, and based at least in part upon said determination, marking the particular content stored in the local cache as invalid; wherein each of the first, second, and third servers comprise at least one microprocessor and memory storing computer instructions for execution by the at least one microprocessor to perform the method as specified above.