Major with a flat 7 — the scale of the b7 chord and the 1⁷ vamp. The moment a progression leans on the borrowed b7 (Mixolydian Drone, the Alabama Loop) or parks on a dominant tonic (Church of the One, any funk one-chord), Mixolydian stops being a mode and becomes simply the notes of the song. Old Joe Clark is this scale wearing a fiddle.