For the sake of simplifying the overall specification, optimizing performance and eliminating unnecessary steps, the existing Cache Service can be simplified by eliminating the need for the list of cache keys to be wrapped in JSON or XML. A simple plain text listing of cache keys separated by a CR/LF is more than sufficient.
example:
POST /api/cache/invalidate HTTP/1.1 Host: example.org Content-Type: text/plain cache-key-1 cache-key-2 cache-key-3
(low priority)