When you no longer need or want it, you can use the SCSI rescan script to remove an unmapped LUN from the host.
You must have a copy of the rescan script. The rescan script is available with the sg3_utils package. In addition, the rescan script is available with Red Hat Enterprise Linux 5 Update 4 or later and Red Hat Enterprise Linux 6 or later, SUSE Linux Enterprise Server 10 SP2 or later, and SUSE Linux Enterprise Server 11, 12, or later. For earlier versions, use the vendor-specific rescan scripts, which are available on their web sites. See the documentation for your HBA.