There are several NMAP probe related Attack Definitions in the IPS policy (Recon Policy if using older NSM version). You would need to look at each to determine whether they can be set to block. I, personally have not had the chance to go through the Recon attacks since they were incorporated into the IPS policy so I do not know if any can be set to block I don't believe the older software allowed you to set any recon alerts to block.
To give you a head start, this KB lists all of the correlation related attack definitions, just do a search for NMAP on the page to see the associated attack definitions.
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