Actually, if you want to work in the score editor the solo tool does scrubbing. I'm not a big fan of the way it works (not a good motion to it), but it does allow you to scrub one or more tracks.
I could not get scrubbing to work in the score editor at all with the scrubber tool or key commands.
I did do some experimenting though in the Arrange window. Below I've quoted from the manual and indented my responses.
Scrubbing Particular Regions
The following list outlines the relationship between scrubbing and region selection:
If no regions are selected, all regions are scrubbed.
It just draws a rectangle and nothing plays
If you select a specific audio region, only it is scrubbed.
Yes.
If you drag to select or Shift-select audio regions on different tracks, only the selected audio regions are scrubbed.
Yes.
MIDI regions (software and external MIDI) are always scrubbed, regardless of the selection status (provided that the Scrubbing with Audio in Arrange project setting is active).
That seems not to be true, at least with the scrubber tool and mouse. If you can select one midi region and scrub in only that one, that would again make the statement false. In fact, it seems if a region isn't selected it won't sound if you use the scrubber tool.
The Mute or Solo status of all tracks and regions has an effect on what you hear when scrubbing, so you can make use of them to scrub audio parts in isolation (or with particular software or external MIDI instrument tracks).
Yes.
MIDI-Controlled Scrubbing
The Scrub by MIDI value (-2-) function (available in the Controller Assignments window; see the Logic Pro Control Surfaces Support manual) is designed to allow scrubbing via external MIDI control. You can assign any MIDI controller number to this function. Data bytes over 64 scrub forward, and those under 64, scrub backward.
Oddly, the scrub controls on my keyboard, which I had assigned to [ and ], did seem to play all midi tracks whether they were selected or not, but NOT the audio track which I selected.
I tried to have scrub forward and backward learn the knob control of my Korg Kontrol, but it seems to recognize one positive number only so it would only go forwards and usually just one little step, so I'd have to keep turning back past 12:00 and go to the right again. Useless. Probably a default of the Korg not sending bytes over 64 as I was getting numbers in the single digit range.
This is progress anyway.
cheers,