I have what is (as far as I can remember) a vanilla Ubuntu installation (v.14.10) using the Gnome Desktop (v.3.9.90), yet I can't seem to get reverse scrolling to work.
There's no option for natural scrolling the basic Gnome mouse configuration or in the Gnome tweak tool. But in
dconf there is an option under:
But this has no effect for me. I've tried several techniques including the ones suggested in the attached issues, with no luck.