Hey
You can build a macro if this is something which is repetitive and you want to perform for every search.
Refer below doc to build a macro.
http://docs.splunk.com/Documentation/Splunk/7.0.3/Knowledge/Definesearchmacros
Build a macro with the following query
index=<your_index> NOT host IN (dx*,idx-i-,sh-i-,c0m1-i-*)
let me know if this helps!
You can using NOT
operator and specify the list of host name (use can use wildcard) you want to exclude
query will be like ,
index=* NOT (host="dx*" OR host="idx-i-" OR host="sh-i-" OR host="c0m1-i-*")