Since it's becoming harder and harder to implement transparent proxies and caches, someone should define a local cache protocol so that network administrators can configure explicit shared caches for the devices on their networks.

> someone should define a local cache protocol

Someone did, almost two and a half decades ago. It's called the Internet Cache Protocol.

- Internet Cache Protocol (ICP), version 2 [0]

- Application of Internet Cache Protocol (ICP), version 2 [1]

--

[0]: https://tools.ietf.org/html/rfc2186

[1]: https://tools.ietf.org/html/rfc2187