ScaleiO offers "Trim" capability which enables the host to instruct ScaleiO to decommission previously provisioned blocks in a volume that are no longer in use.
This can be done for Blocks which are aligned to 1MB boundaries.
Hope this helps,
I do not believe TRIM support is documented at this time.
If the OS supports TRIM, SIO will support it. However, I need to verify this as ESXi support for TRIM in itself seems to be in question.