Hi Rajad,
I feel you don't need to set/configure any value specially to G-page.
Yes, you are right. we must use Global address scheme in the D-flash command registers..
The sample code that was given by you is OK (Thinking that you must have already configured your flack clock register (FCLKDIV) before doing any kind of flash operations)
But to erase a D-Flash sector successfully, you should mention the logical sector addres also..(may be you know this ..) like..
FCCOBIX = 0x00; /* index 0 */
FCCOBHI = 0x12; /* D-Flash Erase command */
FCCOBLO = 0x10; /* Global address value i.e. G-Page value */
FCCOBIX = 0x01; /* index 1 */
FCCOB = 0x0100; /* sector address of a D-Flash */
please check the attached file, it may help you..