I'm not a CFI but according to FAA order 7110.65S Ch. 2-1-16 Surface Areas [http://www.faa.gov/air_traffic/publications/atpubs/ATC/atc0201.html#atc0201.html.8], ATC is required to:
a. Coordinate with the appropriate nonapproach control tower on an individual aircraft basis before issuing a clearance which would require flight within a surface area for which the tower has responsibility unless otherwise specified in a letter of agreement.
b. Coordinate with the appropriate control tower for transit authorization when you are providing radar traffic advisory service to an aircraft that will enter another facility's airspace.
The pilot is not expected to obtain his/her own authorization through each area when in contact with a radar facility.
c. Transfer communications to the appropriate facility, if required, prior to operation within a surface area for which the tower has responsibility.
It brings up another question, what's the best way to handle the situation where you're approaching your flight planned destination, which requires a transition through a nearby airfield's towered airspace, and you're already on flight following, but ATC is busy or just doesn't realize you need a transition? Should you request freq. change for 1 min to contact tower to request the transition, or just remind ATC you require transition assistance?
An example would be a flight like KRHV;SUNOL/Fix;SAC/VOR;KMCC. Sacramento Executive Class D is in the path of dest. McClellan airfield (KMCC), and assuming you're with NORCAL on flight following, and approaching SAC/VOR, but NORCAL hasn't initiated comm withing the last couple of minutes.
BTW, that whole area has more than a dozen airfields in the same 20mile circle. I'm flying to KMCC at the end of the month. Anyone have tips on what to expect trying to land at that airfield, regarding NORCAL comm and pattern entry?