Taking adhesive off floorboards isn't as easy as off screed/concrete. If you had concrete I would have suggested an SDS drill with chisel attachment, but as you have floorboards, it may do a lot of damage. No real alternative but to carefully use a hammer and chisel where you can and then a scraper for the rest.
Either that or cut out the floor boards and put new down. What about levelling it with levelling compound, do you have space for this. Also why did you remove the marble in the first place, were you having problems with cracking etc?
Maybe other guys on here will have better ideas.