SQL Server query

All machines should have three groups(grp1,grp2,grp3) but some have two groups and some might have all three and some might have 1 or zero.

I have data like this, I have two columns:

MachineName   GrpName
Machine1      grp1
Machine1      grp2
Machine1      grp3
Machine2      grp1
Machine2      grp2
Machine3      grp3
Machine4      grp2
Machine4      grp3

I am trying to write a query to see missing groups for all machines from the above data

So Machine1 has all three we can skip or say all three exist

MachineName   GrpName
Machine1      all three exist--if we can do this good if not fine we can just skip since it has all three.
Machin2       Grp3 missing
Machine3       Grp1 and Grp2 missing
Machine4       grp1 missing

Any help on this will be appreciated...