I think ALL, but with some small exceptions. When I was in university for my undergrad degree, the field of study I chose was biogeography, which is the interaction of plants and animals with the land. I was a new Christian, and found out the prof was a Christian. He had long been indoctrinated with evolutionary theory. But then, he went to study the tropical rain forests of Brazil. He said there were small "relic" areas that contained literally millions and millions of plant and animal species. So much more than any of the surrounding jungle, or any place else in the world.
It so shocked him, because he realized that the theory of evolution predicts more and more plant and animal species evolving, instead he was seeing the opposite. He was seeing evidence of a world before the flood. With diversity that is unheard of anywhere else. So, he became a creationist, although long earth. (I'm short earth.)
So, my theory, is that like in Water World, where they finally found land, and it was the top of Mt. Everest, the waters did cover the whole world. Perhaps even the relic areas were flooded, but not as deeply as the rest of the world, and maybe the waters drained from that area first, and most of the animal and plant species survived.
Certainly, it would be nice if this information about these relic areas were more widespread. As it is, these areas are being slashed and burned for large tracts of crops and monocultured trees. For me, it shows the utterly amazing creativity of our Creator God, and how impoverished we are today in our biological diversity.
The fact is, there was a massive flood. There is geological evidence in every rock and land form for a flood. 80% of the world's rocks are sedimentary, that means, laid down by water. We just went to the Grand Canyon a few weeks ago. That massive and awe inspiring place was sedimentary rocks right down to the basement rocks, which were igneous. In other words, rocks that were there before the flood, when all those layers were laid down, and in the most amazing minerals and colours. It was like God said, "Hmm, let's let a lot of sediments build up here." Then he pulled the rocks apart with a little bit of uplift. I did read all the old age evolutionary geology in the various museums and exhibits, but they rang very hollow to me. And I have a good geological background, which was required for my geography degree.
There is also the legends of massive floods all over the world. I'm sure someone dealt with the anthrolopological aspects of the flood. (No, I did not read the whole thread, sorry!) As for the word "all" in the Bible, please remember that the Hebrews, and indeed all the early cultures were not stuck with rigid views of mathematics. There were no computers, no recording of every little geophysical evidence for the flood. The Bible is the history of God. That doesn't mean it is wrong, at all! But it does mean, it was written in terms of how those people thought, not in terms of 21st century North America, in which we demand slavish devotions to clocks, and numbers in everything. That's cultural. As best as Moses knew, and it was passed down, all the known earth was flooded, and it was! In fact, the whole world was flooded. But I believe God left those relic areas, so people would realize what the earth really was like before the flood destroyed so much. And that glorifies God!