HBase is strictly CP (except for its geo-replication, and optional timeline-consistent region replicas).

It uses MVCC for row "transactions" to always keep rows consistent. HBase also has checkAndPut and checkAndDelete primitives, which are atomic, as well as Increment and Append, which are atomic and serializable.

http://hadoop-hbase.blogspot.com/2012/03/acid-in-hbase.html explains it fairly well.

Together with Apache Phoenix you have full multi-row transactions, but they come with a price obviously.