Used memory on Solaris 10

One more question about memory on Solaris 10.

A top shows me that I have 672 MB free memory :

130 processes: 126 sleeping, 2 zombie, 2 on cpu
CPU states: 95.1% idle,  3.9% user,  1.0% kernel,  0.0% iowait,  0.0% swap
Memory: 16G phys mem, 672M free mem, 2048M total swap, 2023M free swap

A vmstat shows me the same :

kthr      memory            page            disk          faults      cpu

r b w   swap  free  re  mf pi po fr de sr rm s0 s1 s2   in   sy   cs us sy id
0 0 0 564744 687896  3  13  0  0  0  0  0  0  0  0  0  354  667  752  1  1 98

But when I do a prstat -a -s size I get this :

NPROC USERNAME  SWAP   RSS MEMORY      TIME  CPU
   45 orbixadm 1449M 1592M   9.7%   4:46:53 0.4%
   48 root      146M  160M   1.0%   8:09:49 1.2%
    3 user1      46M  204M   1.2%   0:00:45 0.0%

    9 webservd   46M   14M   0.1%   0:00:00 0.0%
    5 ctxsrvr    28M   32M   0.2%   4:54:51 0.0%
   11 user2      23M   34M   0.2%   0:00:37 0.2%
    4 user3    4840K   11M   0.1%   0:00:01 0.0%
    1 smmsp    1456K 4552K   0.0%   0:00:24 0.0%
    2 daemon   2128K 6224K   0.0%   0:06:32 0.0%
    1 user4    1232K 3608K   0.0%   0:00:00 0.0%
    1 nagios    376K 2472K   0.0%   0:15:18 0.0%

and as you can see, the sum of RSS values does not reach 15GB of memory, and even if I add SWAP values to it.

So my question is : which command do I believe ?

If top and vmstat give me the good result, where are my 15GB used memory ?
If not, why do they show me that ?

Edit:
the result for the command : % echo ::memstat | mdb -k

Page Summary                Pages                MB  %Tot
------------     ----------------  ----------------  ----
Kernel                    1687138             13180   82%
Anon                       137110              1071    7%
Exec and libs               47107               368    2%
Page cache                  95277               744    5%
Free (cachelist)            22248               173    1%
Free (freelist)             69592               543    3%

Total                     2058472             16081

Physical                  2055442             16058

Edit 2:

Ok, now i can see the memory used by ARC cache.
But with some new tests, now I have :

2066 MB used (prstat -Z and echo ::memstat | mdb -k result)
1193 MB free (top result)
8859 MB ARC cache (kstat zfs::arcstats:size result)

Which give us more or less 12 GB of memory, while my system has 16 GB.
Maybe I missed something else, but where are the other 4 GB ?