I feel like this is a dumb question, but I really don't know how to google this, since every combination of the words 'ScaLAPACK' and 'block' just bombards you with information about the block-cyclic matrix distribution ScaLAPACK uses. However, what I want to know is whether ScaLAPACK subroutines are generally 'blocking' or 'non-blocking' in MPI lingo, i.e. whether or not they wait to finish on all other processes before they return. Sorry again for the stupid question.
Yes, ScalaPACK routines are blocking calls. If you wish to use non-blocking scalapack routines, it is still in its infancy, but I would recommend checking out the SLITE (https://www.icl.utk.edu/research/slate) project.
Hope it helped!