The worst thing you can ever do to hardwood flooring is put a box of kitty litter within kicking range* of it. The dust that the litter leaves behind will not ever fully come off. Not with a dry swiffer, nor with a wet swiffer. Not with a broom, nor with a vacuum cleaner. Not with a rag and some warm water. Not even if you start shouting (at your cat? at fate?) about how you pay good fucking money for these floors, and you take good fucking care of this cat, and there is absolutely NO fucking reason why this should have happened to you. Neither fate nor your cat nor the unholy force binding the litter dust to your floor will be moved by this appeal to fairness.
Now you know.
*Equals the maximum distance you believe your cat should reasonably be able to kick cat sand plus the remaining distance to reach the wood floors.