Least accessing instances show as high memory utilization in my resource monitor

Hi All,

Currently 5 SQLServer instances are running on one of my clustered node and least accessing instances show as high memory utilization in my resource monitor. Can someone advice the reason behind this and way to reduce that. i am using SQLServer 2008 R2

Allocated memory for database instance: 6144 MB

Target Server Memory(KB) 6,291,456.00

total Server Memory(KB)  2,691,632.00

Image                  PID         Hard Faults/sec               Commit (KB)      Working Set (KB)             Shareable (KB)                 Private (KB)

sqlservr.exe       8104      0                                           3,333,880            3,068,244                           47,656                                 3,020,588

Thanks,

robb