If your party is 4x Ret + 1x DK.

Each of the Ret's has:

/targetparty
/cast Cleanse

Then Ret A, can hit Ret B, Ret C, Ret D or the DK.
And Ret B, can hit Ret A, Ret C, Red D or the DK.
And Ret C can hit Ret A, Ret B, Red D or the DK.
And Red D can hit Ret A, Ret B, Ret C or the DK.

No pally will ever hit themself.
But they have 3 pallies which will eventually hit them.
The macro should work pretty well as is.