PHP setcookie domain

Some application, not written by me, and not in PHP, creates a cookie for the domain www.example.com.

I am trying to replace that cookie. So in PHP I did:

setcookie('mycookie','mydata',time() + 2*7*24*60*60,'/','www.example.com', false);

However the resulting cookie is created for domain: .www.example.com, note the dot "." ahead of the domain.

So it doesn't replace it, it creates another cookie. What can I do?