How to find, Is custom Pick list values are bind with Global value set or not using Schema.DescribeField?

Question

In Case object i created 2 custom picklist fields. first picklist value is binded with global picklist value set & second picklist value is given manually (eg., Enter values, with each value separated by a new line).

While running that picklist schema.describe method fro loop i want filter the fields, which picklist field is not binded with global value set.

Code (What I tried)

`List types = new List{'Case'};
            Schema.DescribeSobjectResult[] results = Schema.describeSObjects(types);
        for (Schema.DescribeSobjectResult res : results){
            system.debug('res.length :: '+(String.valueOf(res)).length());
            system.debug('res :: '+res);
            for (String field_name : res.fields.getMap().keySet()){
                for (Schema.PicklistEntry pklst : res.fields.getMap().get(field_name).getDescribe().getPicklistValues()){
                    system.debug(pklst);
                }
            }
        }`

What I want (Expected output)

While running that picklist schema.describe method fro loop i want filter the fields, which picklist field is not binded with global value set. note: Using Schema.Describe method. not tooling api.