There is no need for erasing full flash, It's more simple to rewrite EFS, using eMMC plugin. RIFF JTAG Box FAQ - How to use QUALCOMM eMMC MBR/EBR Partitioning plugin
But, if You really want to erase eMMC chip, You can in fact only null erase it. Basically, it would write 00 00 00 00 ... content to all or selected partitions.
Here is procedure:
- Launch eMMC Plugin
- Click "Load image from device"
At this point, plugin will read partitions (ebr/mbr table) from phone, and create and empty file dump, filled with 00 00 00 00 . . .
- Select partition You want to null erase
- Click "Flash Selected"
This procedure will take time, because it's practically flash procedure. Simple erasing on eMMC chips is DISABLED.