Do you have any experience / recommendations / best practice on how to update server-side data residing in a Cache database via a REST service?

A naïve approach would be to send a full JSON representation of the data object via an http POST to a method on a REST handler class:

<Route Url="/mydata/:id" Method="POST" Call="Update"/>

The problem I see here is, if only one of the data object's properties has changed, how do we know which? Or do we simply overwrite all properties?