How about...

Update table1 set col1 = col1^1

I agree that if you pass a comma-delimited string to the sproc that the coalesce method I posted will not work.  But, if the possible values are a single dept...

Maybe I don't completely understand the problem, but...

Create Procedure FillReport

(

    @Dept varchar(20) = null

)

AS

BEGIN

     Select [whatever] from [someobject] where Department = COALESCE(@Dept, Department)

END

GO

Pass a null value to the sproc when...