Views Grouping by Field
I'm not sure if you've had this answered yet, but in Drupal 7 and the latest version of Views, this is possible by doing the following:

Under Fields, click the one you want to configure, in your case it probably looks something like:
Content: Departments

Select Multiple Field Settings and it will drop-down to where you see a check mark in the box labelled:
Display all values in the same row

Uncheck this box and it should list your members twice, once in each department they are specified under.