It would serve you better to forget scales in the riffs. They typically throw conventional scales out the window... I know my band did. Just remember that the flat 5 is your friend and it's all good. Not necessarily in a chording sort of way but in an interval sort of way.
I suppose Tritonus Diabolica would fall into what you are looking for. (Lydian scale (4th mode of C major): C, D, E, F#, G, A, B, C.
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