With a high-enough PR, when I Mind Scan I can also perform a Mind Probe on the target. But can I do this even if I didn't purchase the Mind Probe power?

No.

Your mind scan identifies targets nearby. If you do well enough you have pinpointed a mind well enough to then use mind probe against the target, but it does not automatically mind probe. I would rule you gain a free action to cast mind probe, but you must have the power to use it.