Erase Vlan Data - Cisco Switches

When resetting switches to factory default it's important to note that Vlan information from switches in any mode except transparent mode switches store their Vlan information in a vlan.dat file in their flash memory. If the switch is in VTP transparent mode then the Vlan configuration could also be stored in the running configuration as well as the start up configuration

Delete Vlan information commands

Remove the vlan.dat file (Only command required for a VTP server\client mode switch)
SW1 > enable
SW1#delete flash:vlan.dat

Clear startup\running config
SW1#erase startup-config

Erasing the startup-config and reloading inherently removes the running config if the changes are not saved before reload.