Can A.com access the cookies stored by B.com website ?
If yes then how ?

One possible option is that A.com behaves like a client and change its browser settings and manually or randomly add an entry in cookie database stored in our browser
that means random integer is set as cookie number for B.com then if that number exists in B.com database then the A.com can see what information has been stored related to that cookie ?

I dont know whether its possible or not but if it is possible still it does not tell A.com any information about the customer having this specific cookie number.
Please discuss....