MMC read write cycles

Hi,
Anyone know about MMC cards?

I have found they have an endurance of 300,000 write/erase cycles but does this mean

A) if you write 1 byte to address 0, 300,000 times the whole card will then fail?

b) If you write 1 byte to address 0 300,000 times, only address 0 will fail?

Thanks