Hi, I have removed marble tile from my entry way for the purpose of putting wood floors down throughout the house. I didn't realize that 2 inches under the marble tile would be what seems to be a sand bed before getting to the cement foundation. For the sake of putting down a glue down wood floor on top, what do I need to do to that 2 inch bed after having removed the sand to prepare for putting down the wood flooring?

I've heard several different opinions so need some more please!