A quick fix would be to rub a walnut, not the shell, the meat into the scratch. I have used this on furniture and other wood surfaces and it helps to hide it.
I found shoe polish close to the color of your floorboards is a great cover up
I heard that you can make a mixture of sawdust and glue(the kind that is used to connect peaces of wood) and fill the hole with it..
I agree with Judy Grecco's suggestion of using a walnut. It's something I do a lot and it works great for my medium stained wood floors.
Here is what i use, on furniture or floors.OLD ENGLISH scratch cover for dark woods works great. Or they have pens at menards for wood to match the color of your floors. I have tried both and they work great.
Don't know if it will work, but try steam. Use an iron over damp paper towels or wash cloth. Don't lease the iron the cloth too long but keep checking. I know it works for dings in furniture.
If the scratch is very deep and noticeable, a bit of wood filler mixed with a colour stain that matches your floors should fix it.
Also try WATCO's Rejuvinate.
Thanks everyone for your great tips! Much appreciated.