Q: How does one set up an Apple TV to work with Home Kit?

I have the latest iOS (as of 7/29/15) installed on a third-gen Apple TV, and I've signed in with my Apple ID on that Apple TV.  I've installed a Lutron Caséta Smart Hub and light switches, all of which are able to be controlled by Siri when I'm at home and on the same network.  But the Apple TV is somehow supposed to allow me to use Siri when I'm elsewhere in the world, using any network at all.  So far, I can't get that to work. Just to clarify, I can use my cellular network and successfully control the Lutron devices by using the Lutron App, but in order to use Siri, I have to be at home.  Has anyone figured out how to use Siri from elsewhere?