Hi Subbu,
> We found that oracle data buffer quality is 84.1% in our production system.We have to increase this to 95%.
Who says that you have to (maybe EWA)? This sounds like the classic "compulsive tuning disorder". For more information you can check out the white paper "Why a 99%+ Database Buffer Cache Hit Ratio is Not Ok".
If you want to you can run a script that pushes your Oracle data buffer quality up top 99 % (or above) without adding one byte of memory to buffer cache. 
Sounds cool and your target is reached, but does it makes sense? I don't think so.
Regards
Stefan