Address    Orgname
Address1   Orgname1
Address2   Orgname2
Address2   Orgname2
Address3   Orgname3
Address3   Orgname4

Address    Orgname
Address1   Orgname1
Address2   Orgname2
Address3   Multiple

SELECT DISTINCT [Match Address],
CASE WHEN [Match Address] in
    (SELECT y.[Match Address] from
        (SELECT x.[Match Address], count(x.ORGNAME) as [Count] from
            (SELECT DISTINCT [Match Address], ORGNAME
            FROM Table) x
        GROUP BY [Match Address]
        HAVING count(x.ORGNAME) > 1) y)
THEN 'Multiple' ELSE ORGNAME END as ORGNAME
FROM Table