How do I remove a linked device that has been sold?

I sold my desktop and laptop but forgot to remove them from my synced iCloud devices.

I did tell the new owners to set up iCloud which would have removed them from my account but they never did it.

I've even sent them a message via "find my devices".

I can see them on "find my devices" and I can see changes being made in my bookmarks on my existing computers.

For now I have unlinked my current computers to the cloud. I'd like to start using the syncing functions of iCloud again but first I need to remove the two computers I sold.

Is there a way such as in iTunes where you can deauthorize all devices and start from scratch?

Would simply changing my password work? I'd rather keep my password but if I have to change it I will.

(if there is a better forum for this question, please let me know)