The stronger the chemical, the less scrubbing needed. The most effective thing would be something like EZ-off oven cleaner (sodium hydroxide solution if you're not in US). You should be able to spray, let it sit, and wipe off, but make sure you wear rubber gloves as it can burn bare skin. If you don't like strong chemicals, I've heard people use baking soda+water, barkeepers friend, dawn dish soap, lemon juice, or vinegar. Other brands/types of oven cleaner/degreaser would fall somewhere in between the above two options, they don't vary too much apart from special cases like the EZoff