ZPR[Zero Page Reclaim], reclaims space where there are either no blocks written or the deleted blocks are 0'ed out. With the exception of some supported hostmodes on Filesystems like Vmware.
I tried to see if I could find something about filesystems that are supported but couldn't find something quickly. What filesystem are you using? Most of the time the File System wont write 0's or let the storage system know that it deleted the data it will merely dereference them from the file allocation table.
If all fails, one thing you could try(if you're using LVM in Solaris) is to vgextend onto a newly created volume and then shrink the existing volume out of the vg. LVM should only copy the currently used blocks to the new volume[basically LVM will discard the unused blocks]. You could then, deattach the old volume, double/tripple check that everything is working and then delete the old volume and reclaim the space that way.