HTTP Status 204
This was new to me. The HTTP Response header can use a status code '204 No Content'. This tells the user-agent not to expect any response content, and so to not refresh the current page. For simple interactions where you want to keep the server current on a users selections it looks useful.
Here's some (old but interesting) browser test results. There's apparently some disagreement on whether response content accompanying a 204 is an error, or should just be ignored. The safe bet seems to be to not send any content body.