Scooby is a simple term derived from the combination of the words "It's cool B." Basically it can mean that you're okay with something, or it can be a question asking if someone else is okay with something.
Person 1: We bout to go to the movies, scooby?
Person 2: Scooby.
Person 1: We're going to the movies, is that ok with you?
Person 2: Yes that's ok with me.
Somebody close to you. A good friend. Probably derives from the real word doula that refers to somebody who is there for a pregnant woman emotionally and physically through her pregnancy. In the slang tense it is somebody who's there for you that you can always count on.
I known that dude my whole life, that's my doula for real.