Alex,
All SFR's are set to predetermined values after power up or a reset assertion on the reset pin.
Internal ram is not affected by a reset assertion on the reset pin.

During power up, internal ram is indeterminant.

So, you could in theory, if you wanted, write a value to an internal ram location and test it during start up.
If the value is the one you wrote then you probably had a reset occur.

That being said for completeness, I highly advise against it. It would not be a wise move to test a variable that COULD match yours after a power up.

Your best solution is to catch the condition in hardware and have the 8052 test that during start up.

Allen