What most naturally follows?

How to stop a cat from scratching the couch
To put an end to this immediately, it is necessary to put something solid-like a door-between your cat and the couch (or any other item he is scratching inappropriately.
This is a temporary measure. The cat can be reintroduced to his entire domain after these other steps have been accomplished.
If there is no way to isolate the cat, it would be best to put something heavy (heavier than the cat) up against the damaged furniture. Something like an end table, a chest, a wall, or even a cinder block or two.