In the reading I have done (limited) on the period of earlier ancient Greece, I found little reference to cavalry. I. E. at Marathon, they were using runners to send word back to Athen's of their victory (Niki!).
I would say if there are two things a commander wants, more so needs to get as soon as possible; First its information on the strengths and location of the enemy and second, when and if your reenforcements are going to arrive.
Point being; If cavalry were a major part of these armies of Greece, I would think, first and foremost, it would have been in the way of scouts.
"You see old friend. I brought more soldiers than you did." *Leonidas-300