Find what data is placed in a datafile
The following SQL will show you which file groups your tables and indexes are in which will make it easy to see if there is data in any file group that shouldn't have data.

SELECT      f.[name] AS FileGroupName
            , o.[name] AS ObjectName
            , o.[type] AS [Type]
            , i.[name] AS IndexNAme
            , i.[index_id] AS IndexId

FROM        sys.indexes i
INNER JOIN  sys.filegroups f ON i.data_space_id = f.data_space_id
INNER JOIN  sys.all_objects o ON i.[object_id] = o.[object_id]

WHERE       i.data_space_id = f.data_space_id
            AND o.type = 'U' -- User Created Tables

ORDER BY    f.[name]
            , o.[name] 
            , o.[type] 
            , i.[name] 


full details of the script can be seen here