Removing Duplicate Delimited Values From A Single Column?

I have a stored procedure that returns a single row based on a parameter of employee ID. This particular procedure uses a CTE to traverse our org structure. One of the columns is returning a delimited string of Windows login values and due to the business rules, it can contain duplicate values. I need to have that column contain only unique values - no dupes.

For example, this one column could contain something like this:

domainuser1;domainuser2;domainuser2;domainuser 3;

The need is to convert to this:

domainuser1;domainuser2;domainuser3;

I know that's a tall order.