I don't think it is at all controversial (I'll try and find some material on this later). It's quite certain that a very small number of humans (perhaps less than 500... likely less than 250) left Africa and ended up populating the rest of the available land mass (everyone of "non-African" descent). That means that "all of the modern human genes" pretty much stayed in Africa with most of the modern human populations that never left.
You're probably thinking of the Toba super eruption. I think we've discussed it before, but there is a hypothesis that the Lake Toba super volcanic eruption 74,000 years ago was the cause of a severe species-wide genetic bottleneck which geneticists think occurred somewhere between 60,000-80,000 years ago.
This is one of the biggest unsolved mysteries and the genetic evidence is starting to contradict itself (different results in different studies) and some genetic evidence contradicts the archaeological evidence. I'll try and post some links discussing the problems tomorrow. The dates differ from 60,000 to 120,000 years ago.
Fair enough. I know you're referring to something other than Toba, but since Toba fascinates me I'd love to know how the two potential bottlenecks working in tandem ended up narrowing the gene pool in more detail. I just need to read a lot of books on the subject when I next have a break.