Removing old hard caulk

We just recently moved into a new house and the master bath shower needs to be re-caulked.  It is cracked really bad with gaps large enough to make it so that we won't use the shower until it has been taken care of.  I went to try to remove what was there but it is rock hard.  At first I was even thinking they may have just used grout it was so hard.  I have tried just about everything I have and nothing is working.  Even a razor blade can hardly score it.

Is this the job for an oscillating tool (i've been looking for an excuse to get one anyway)?  Or is there something else that I should try?

Thanks.

A 5-in-1 with a hammer may work but be careful not to make scratches. 

Have you tried contacting an expert? It won't hurt if you do so.

I had the same issue at our house.  I tried scoring with a razor blade as much as possible but had to resort to a screw driver and hammer...just be careful where you set the screw driver and at what angle!

I think using a screwdriver and a hammer would be a perfect solution. Even if you do end up making damages in areas you didn't intend I can't imagine these damages would be difficult to repair either. Let us know how it goes!