This question highly depends on how you'd define a genocide. Colonization of the Americas brought about great destruction of many different Native American groups, but it was not so much an intentional campaign like the Holocaust or Armenian Genocide, so much as it was the consequences of a new people pushing the Natives out of their lands and giving them diseases (mostly unintentionally).

The Jangil people of the Andaman Islands were rendered extinct by colonization. Again, same deal - it wasn't exactly a campaign focused on eradicating people. The Beothuk of Newfoundland are another example. There are other examples I'm sure.

Genocide is not an easy task to carry out - people will flee, fight back, etc.