Global can be shared by all namespace

4 options:

• map it to namespace %ALL
• naming it with  % as first character places in %SYS namespace (e.g. ^%MUTHU) 
  • that traditional approach is possible but not recommended
• naming it ^mtemp.*,  ^CacheTemp*, ^IRIS.Temp* allocates it in db IRISTEMP
• subscript level mapping allows partial mapping  (e.g. to IRISTEMP)  

I will say create a new database named SHARED

Create Global in that database like ^MUTHU (without %)

Add mapping in %ALL namespace (if there is no such namespace then you can create)

[Map.%ALL]
Global_MUTHU=SHARED

now you can access this global from all namespaces.