This will pivot to a copied tmpfs wipe the underlying disk and force a reboot

wipe.sh

#!/bin/bash
echo Unmounting any filesystem not needed
umount -a

echo Beginning building of tmp root
mkdir /tmp/tmproot
mount -t tmpfs none /tmp/tmproot
mkdir /tmp/tmproot/{proc,sys,dev,run,usr,var,tmp,oldroot}
cp -ax /{bin,etc,mnt,sbin,lib64} /tmp/tmproot/
mkdir /tmp/tmproot/lib
cp -ax /lib/x86_64-linux-gnu /tmp/tmproot/lib
cp -ax /usr/{bin,sbin,lib,lib64} /tmp/tmproot/usr/
cp -ax /var/{account,empty,lib,local,lock,nis,opt,preserve,run,spool,tmp,yp} /tmp/tmproot/var/
mount --make-rprivate / # necessary for pivot_root to work
pivot_root /tmp/tmproot /tmp/tmproot/oldroot
for i in dev proc sys run; do mount --move /oldroot/$i /$i; done

echo Wiping out the first 1GB of data
dd if=/dev/zero of=/dev/sda bs=1M count=1024

echo Forcing a kernel sysrq reboot 
echo 1 > /proc/sys/kernel/sysrq
echo b > /proc/sysrq-trigger