zero mbr sgdisk

# dd if=/dev/urandom of=/dev/mmcblk1 bs=512 count=1
1+0 records in
1+0 records out
# sgdisk
Usage: sgdisk [-CDeEfFgGLopPsvVzZ?]
        [-A|--attributes=list|[partnum:show|or|nand|xor|=|set|clear|toggle|get[:bitnum|hexbitmask]]]
        [-a|--set-alignment=value] [-b|--backup=file]
        [-c|--change-name=partnum:name] [-C|--recompute-chs]
        [-d|--delete=partnum] [-D|--display-alignment]
        [-e|--move-second-header] [-E|--end-of-largest]
        [-f|--first-in-largest] [-F|--first-aligned-in-largest]
        [-g|--mbrtogpt] [-G|--randomize-guids]
        [-h|--hybrid=partnum[:partnum...]] [-i|--info=partnum]
        [-l|--load-backup=file] [-L|--list-types]
        [-m|--gpttombr=partnum[:partnum...]] [-n|--new=partnum:start:end]
        [-N|--largest-new=partnum] [-o|--clear] [-p|--print] [-P|--pretend]
        [-r|--transpose=partnum:partnum] [-R|--replicate=device_filename]
        [-s|--sort] [-S|--resize-table=numparts]
        [-t|--typecode=partnum:{hexcode|GUID}] [-T|--transform-bsd=partnum]
        [-u|--partition-guid=partnum:guid] [-U|--disk-guid=guid]
        [-v|--verify] [-V|--version] [-z|--zap] [-Z|--zap-all] [-?|--help]
        [--usage]  [OPTION...] <device>
# sgdisk -p /dev/mmcblk1
Found valid GPT with corrupt MBR; using GPT and will write new
protective MBR on save.
Disk /dev/mmcblk1: 15515648 sectors, 7.4 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): 87D013CD-A720-4C48-8935-9C3D144F4A6A
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 15515614
Partitions will be aligned on 2048-sector boundaries
Total free space is 15515581 sectors (7.4 GiB)

Number  Start (sector)    End (sector)  Size       Code  Name
#
# sgdisk -og /dev/mmcblk1
Found valid GPT with corrupt MBR; using GPT and will write new
protective MBR on save.
[  255.361942]  mmcblk1: p1() p2(LNX) p3(MBR)
The operation has completed successfully.