It really depends on how you define genocide.

Does it have to be the formulaic "holocaust" genocide, going door to door and rounding up everyone of a certain ethnic background for extermination?

This is extremely unlikely to ever work unless it was done to a very small population, such as /u/thebrainslug pointed out with the Tasmanian Aboriginals.

There are plenty of cultures/peoples who were crushed in battle/by cultural movements that were essentially wiped out, either intentionally or by natural course.

"Race" is a problematic term for a variety of reasons.