You can use the SCSI rescan script to remove an unmapped LUN from the host. This is required to remove stall entries of LUNs on the host and remove confusion between mapped and unmapped LUNs on 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, Red Hat Enterprise Linux 6.0 or later, SUSE Linux Enterprise Server 10 SP2 or later, and SUSE Linux Enterprise Server 11 and 12 or later. For earlier versions, you can use the vendor-specific rescan scripts, which are available on their web sites. See the HBA vendor-specific documentation.