Erase macbook pro

I have 2 MacBook pro. My personal computer and one from work and both on the same apple id.

I need to return my work computer after I erase all it's files now.

What I am worrying about is that after the last mac update, all my computers files were combined and I could see one computer on another without even opening the cloud.

I am worrying if ill erase one it will harm the other one.

Any thoughts ??