You can filter using search command. Ideally you should include the hosts you need rather than excluding the hosts you don't need. You can use AND and OR for adding a list of hosts. Following example will exclude all servers starting with abc like abc01, abc02 etc.
| metadata index=Test_app type=hosts
| search host!="abc*"
| eval age = now()-lastTime
| where age > (60)
| sort age d
| convert ctime(lastTime)
| fields age,host,lastTime
Following will not include servers abc, def, ghi. Like stated earlier, performance wise, it is better to include required fields values rather than excluding the values not required.
| metadata <Your Base Search>
| search host!="abc" AND host!="def" AND host!="ghi"
| <your remaining search>