Just received a fail event from mdadm (UncorrectableError), is my drive dead?

["Mike Garey" <random51k@gmail.com>]

I just received an email from mdadm monitoring saying that "A Fail
event had been detected on md device /dev/md0." According to dmesg, I
see the following:

hdc: dma_intr: status=0x51 { DriveReady SeekComplete Error }
hdc: dma_intr: error=0x40 { UncorrectableError }, LBAsect=84672935,
high=5, low=786855, sector=84672935
ide: failed opcode was: unknown
end_request: I/O error, dev hdc, sector 84672935
raid1: Disk failure on hdc1, disabling device.
       Operation continuing on 1 devices
raid1: hdc1: rescheduling sector 84672872
RAID1 conf printout:
--- wd:1 rd:2
disk 0, wo:0, o:1, dev:hda1
disk 1, wo:1, o:0, dev:hdc1
RAID1 conf printout:
--- wd:1 rd:2
disk 0, wo:0, o:1, dev:hda1
raid1: hda1: redirecting sector 84672872 to another mirror

cat /proc/mdstat shows the following:

Personalities : [raid1]
md0 : active raid1 hda1[0] hdc1[2](F)
     158577472 blocks [2/1] [U_]

unused devices: <none>

does this mean my drive is dead and should be replaced?  Or is it a bad
block that's been remapped to another part of the drive, and I just
need to re-add my drive to the array to get it to re-sync?  Thanks,

Mike