How does a cache handle overwriting between 2 addresses in the same block?

Consider a byte-addressable cache with block size 16 bytes, bytes 0-15 form one block. First I write an int(let’s say 7) to address 0, so now bytes 0-3 contain the int 7. Now if I try to write another int(9) to address 2, then how does the cache handle this? Also if i try to read from byte 1, what effect does that have?

The lectures I’m watching suggest treating a block as the atomic unit in a cache, because keeping track of all the unwritten and written bytes will be a resource heavy task. So how will the above situation pan out? Will every block contain only 1 instance of data, with every write beginning from byte 0? because that is the only possible solution i can think of.