The present invention is directed to a method for updating a cache. A server identifies whether certain preconditions have been met for a document in a cache from freshness parameters associated with a document identifier for the document. Then when the preconditions have been met, a first document content is retrieved from a remote host. A first content fingerprint for the first document content is calculated. The first document content is stored in the cache. Then a content difference is calculated between the first document content and a second document content, both associated with the document identifier. The content difference is stored. Then the document identifier is associated with the content difference.