how to update billions of docs

[Mohsin Beg Beg]

Hi,

I have a requirement to replace a value of a field in 100B's of docs in 100's 
of cores.
The field is multiValued=false docValues=true type=StrField stored=true 
indexed=true.

Atomic Updates performance is on the order of 5K docs per sec per core in solr 
5.3 (other fields are quite big).

Any suggestions ?

-Mohsin