Oil soap and all-purpose cleanser remove some stains, especially when the spill is fresh. But it's impossible to scrub out stains that have soaked into the wood fibers. And sanding only creates a depression in the floor that's more noticeable than the stain.
The only option is to cut out the stained floorboards and install new ones. We replaced a couple of boards from a standard 3/4-in.-thick x 21/4-in.-wide oak-strip floor using a drill, circular saw and sharp chisel.
To determine the exact width and thickness of the pieces you'll need, lift up a heat register or threshold and measure the exposed ends of the floorboards. You'll find hardwood flooring at a local millwork shop, lumberyard or floor-covering store.