Hm...I wonder if Carthaginians or the Phoenicians count.

Do you mean a ethnic group that had been completely killed off or through integration lost their culture identity count as well?

Ethnic cleansing isn't killing an entire ethnic group. You can ethnic cleanse a region without killing anyone, it's just removing them for a specific area.

This is a difficult question to answer because one has to question what qualifies as ethnic cleansing, and even more speficically, an ethnic group. Do 'sub-groups' count? Does purposeful assimilation count, or just pre-meditated murder? Does simply causing their extinction through avarice and indifference count?

Let's assume that all of these count. The easiest examples to find are among aboriginal groups in North and South America, where several were essentially wiped out. The Kalinago/Caribs of the Antilles would be the most telling example, as they were essentially worked to death (certainly with indifference, although possibly with prejudice). There are several other examples, particularly among tribes in the North East that simply no longer exist. And then, one needs to consider whether the forcible relocation of entire cultures to new (and essentially barren) lands is also a form of ethnic cleansing; many would argue it is.

Of course, if we want to restrict our definitions to more modern examples, one need not look far for sub-groups being wiped out. How many Volga Germans remain, as an example? Or, how many 'Ainu' in Japan remain? Some might argue these as ethnic cleansings of course.

If we step back and only consider ethnic cleansing to encompass deliberate and violent action against an ethnic group (and discount sub-groups/populations) then no single ethnic group has been killed off completely. However, by more broad definitions, there are several ethnic groups (and sub-groups) that, if not eliminated over the last century, have been reduced to the point that their continued existence is in doubt. These are not largely murders, but rather, cultural assimilation, often forced, either directly or economic necessity. For many of these cultures, new policies mitigating the assimilation and actually encouraging the relearning of their culture and language has been put in place, something particularly strong in Europe (where, admittedly, some of the worst assimilation and ethnic cleansing has occurred in the past, obviously influencing these decisions somewhat). But many groups continue to slide into extinction around the world.

By most reasonable definitions the holocaust probably worked IMO. The Jewish population in Germany is still pretty well non existent I believe, though that's less true in occupied countries.

Removed as a "throughout history" type question which is against our rules.