Keeping your bike clean and undamaged is desireable. In most cases, the intended use of a bicycle is riding it, but crashes and accidents do occur. If your bike frame is aluminum or carbon fiber, you don't need to anything if you don't want to, providing that the scratch hasn't compromised the sttructural integrity of the frame. If you have a steel frame and the scratch is through the primer coat to the bare metal, you might want to clean the area that the scratch is in and use touch up paint to cover the bare metal to prevent rusting.