Flushing DNS cache for just one domain

I want to flush Knot’s DNS cache for just one domain. According to the documentation, it is simply cache.clear('foo.example'). But it fails:

> cache.clear('foo.example')
error: Function not implemented

A general cache.clear() works fine. Why is this function not implemented on the Turris while it works for Knot?

It’s implemented since kresd 3.0.0. Stable Omnia has 2.4.1 ATM, but Omnia with Turris OS 3.11+ has it (now in RC).