If you need to factory reset a Cisco switch and delete all of the configuration follow these steps:

Power on the switch while holding the mode button on the front until you get this promt and enter "flash_init":

Xmodem file system is available.
The password-recovery mechanism is enabled.
The system has been interrupted prior to initializing the
flash filesystem. The following commands will initialize
the flash filesystem, and finish loading the operating
system software:
flash_init
 boot
switch: flash_init

If it is done delete the config and vlan files

mifs[5]: Bytes available : 248832
mifs[5]: mifs fsck took 1 seconds.
 -- MORE --
mifs[6]: 566 files, 19 directories
mifs[6]: Total bytes : 57931776
mifs[6]: Bytes used : 28429312
mifs[6]: Bytes available : 29502464
mifs[6]: mifs fsck took 21 seconds.
...done Initializing Flash.

switch: del flash:config.text

Are you sure you want to delete "flash:config.text" (y/n)?y
File "flash:config.text" deleted

switch: del flash:vlan.dat

Are you sure you want to delete "vlan.dat" (y/n)?y
File "flash:vlan.dat" deleted

Reboot the switch and you are done

switch: boot

Loading "flash:c2960s-universalk9-mz.122-58.SE2.bin"...
--- System Configuration Dialog ---
Enable secret warning
----------------------------------
In order to access the device manager, an enable secret is required
If you enter the initial configuration dialog, you will be prompted for the enable secret
If you choose not to enter the intial configuration dialog, or if you exit setup without setting the enable secret,
please set an enable secret using the following CLI in configuration mode-
enable secret 0 
----------------------------------
Would you like to enter the initial configuration dialog? [yes/no]:
% Please answer 'yes' or 'no'.