I'd take this concept one step further. Not only play the scale two octaves, but the full range of your instrument, starting on the lowest note of that scale on your instrument and playing to the highest note of that scale on your instrument. For example: on the piano playing a C major scale you would start on an A and end on a C. Scales are not just good soloing tools, but they help you develop dexterity, agility, and familiarity when you play.