Scratching an itch is far more common than itching a scratch. Both are grammatically correct, but the latter is considered informal. This is part of a complete episode.
gated adj.— «The new study suggests that itch, like pain, may be a “gated” system in which signals from other nerve cells can interfere with or moderate the sensation. Scratching the skin near, but not directly on, the spot that itches...
gleek v.— «What is gleeking? It is when you can spray a stream of liquid from underneath your tongue. Sometimes, you may have done it by accident while eating a sour candy—liquid does a quick spray from underneath your tongue. But I can...